Method and device for determination of the wear resistance of a surface

ABSTRACT

A method and apparatus for determining the wear resistance of the surface of a sample object includes an abrasive grinding belt, run between the sample object and a counter-body, with the grinding belt being pressed against the sample object with a predetermined force by the counter-body. The position of the counter-body is determined at, at least, a first position and a second position, each occurring at two different points in time. The wear resistance of the surface of the sample object is determined from the difference in determined positions.

The present invention relates to a method and a device for determining the wear resistance of abrasively or adhesively strained surfaces, for example thin layers. Methods of this kind are necessary for all types of technical surfaces, which are strained abrasively or adhesively, in particular for tribologically-coated surfaces, for measuring their wear resistance.

The determination of the wear resistance of very thin surface layers is gaining importance very quickly as considerable miniaturization efforts are made in many technical areas, and innovative technologies are growing, like for example the micro-system technique. Micro-Iribological optimisations of rails, bearings and sliding contacts require for example the use of extremely thin layers, which thickness is very often on the sub-micrometer scale and which have to be investigated and optimised by measuring techniques concerning their mechanical wear resistance. Currently there are no appropriate procedures for this problem.

The known micro-scratch tester based on the AFM method is not suitable for the determination of practically usable and transferable results since the scratch results, which are gained with the help of a thin needle, permit no conclusion about the actual areal wear in practice.

For the local resoluted examination of wear characteristics on material surfaces the ball wear method is used. Here calotte shaped grindings are produced by the 3-body-contact on the surface, which is to be measured. Optically measured the grindings allow conclusions about the wear resistance. The grinding is produced by a ball turning on the material surface, which is moistened with a polishing slurry.

It is disadvantageous, that the polishing medium can change its grinding characteristics by being soiled with abraded material, by deposit of particles and by evaporation losses of the fluid. The polishing slurry can furthermore operate as wear passive when particles deposit in soft surfaces and it is unevenly spread over the counter-body's contact route. The surface of the ball is also altered. A frequently change of balls is necessary.

Furthermore this method of load variation is limited by a reduction of the calotte radius. Also the pressure force of the ball can only be used restrictively. When evaluating the measurement, failures of the calotte form (especially rounding of the edges) can falsify the measurement results.

Altogether it is to say, that all the mentioned testing methods supply only limitedly transferable results for each application (scratch-test) or that they cannot be restricted to smaller lateral analyse areas (sand trickle test).

Using the refection method for testing lacquers, the results show great dispersion, while the Taber test does not allow an analysis of extremely thin surface areas.

A further testing device for determining the abrasive wear resistance of magnetic heads in video recorders is published in Bushan, B. et al. “Tribology and Mechanics” Sp. 22, ASLE Spec. Publ., Park Ridge, 1987 from van Groenou et al. In this so-called “Sphere-on-Tape-Test” a tape with an abrasive effect is run between a sample surface and a lateral fixed, weight loaded counter-body ball. The abrasive tape is pressed on the sample by the pressure of the counter-body ball, so that a wear calorie is formed on the sample surface. The sample is now taken out of the device at different points of time and the depth of the calotte is measured.

With this device for example deviations of the tape thickness or complicated topographies of the samples are leading to damping difficulties. Furthermore no exact sample positioning control is possible and due to the removal and fixing of the sample in the device an automation of the measurement is not feasible. So no in situ wear measurement is possible.

The purpose of the present invention is it, to create a device and a method for determining the mechanical wear resistance of a sample surface, which can also be used for determining the wear resistance of extremely thin surface installations and coatings reliably, at favourable costs and quickly.

This purpose is fulfilled by the method as per patent claim 1 and by the device as per claim 17. Advantageous further descriptions of the method according to the invention and the device according to the invention are presented in the claims subject.

According to the invention the present method differs from the prior art by determining the position of the counter-body at at least two different points of time. The advantage of this is now, that not the depth of the wear calotte after removing the counter-body, but directly the position of the counter-body in situ during the wear test is measured. So that then the depth of the wear calotte in the sample's body can be determined from the position of the counter-body.

The increase of the depth is correlated to the wear resistance of the sample surface. With this a simplified measurement and interpretation of the wear measurement is possible.

The used appliances can be constructed small and mobile, although a measurement is possible on big and on small objects.

Measurements of surface areas up to a dimension of 10 nm respectively local measurements on surfaces down to 10 μm² are possible. Wear measurements on the edges of a sample are feasible with this method. By an appropriate controlled load on the counter-body, standardized work parameters as well as an elimination of the influence of thickness variations of the wear belt are practicable.

The method according to the invention can be utilized manifoldly. It can be used, for instance during the quality control and in the field of research and development, for example for lacquer coatings, for the sealing of floors, for the quality control of micro-edifice elements (MEMS) or in the micro-system technique. Particularly, a fast assessment of wear hard-material-layers in the field of coating techniques (galvanizing, varnishing, material coating procedures in general) is possible. It also can be used as optimisation tool during the layer process development (e.g. in the field of galvanic, CVD, PVD).

Since the determination of the position of the counter-body can be made in situ, the tape thickness variation can be eliminated from the measurement by running back the belt into the same position at the respective measurement points of time. So the position of the counter-body is always determined with the same tape thickness. The measurement of the counter-body's position can be made when the tape is stopped at one patch of the tape, which has not been used for generating wear. This has a particular importance, when calotte-depths are measured in a range of 10 nm, while the tape thickness is usually >10 μm (typically 10-20 μm) and amounts so up to a thousand times of the produced calotte-depth. This also enables the resolution of calotte-depths of a scale of 1 nm. Customary magnet tapes can be used as tapes, which enable the marking and recognizing of a certain tape position, so that the belt can be run back into the marked position for the single measurement points of time without pressure or load and, if applicable, without further contact to the counter-body and/or the sample surface. Of course, also a position, which is relatively staggered to the measurement position of the tape, can be marked. The utilized grinding belts are in this case advantageously conventional audio or videotapes with a RMS roughness of 10 to 30 nm. In the case of magnetic tapes the marking of the tape position used for the measurement can be made and/or recorded magnetically. As holding and transport device for this belts customary tape transporting units like VCR or MC drives can be used like for instance from mobile devices.

The measurement of the counter-body's position can be made capacitative, inductive or interferometric. In the last case the counter-body itself can be equipped as reflector. The force on the counter-body for pressing the tape against the sample surface can be produced capacitatively (AFM), magnetically or also inductively (touch method). The adjustment of the force can be done very flexible using this method, so that the damping behaviour is controllable and even with higher belt speeds micro-calottes with an extraordinarily good surface smoothness without grind grooves are produced. For the magnetic generation of force, permanent and/or electro magnets are suitable.

The counter-body can be a ball or a cylinder. When using a rolling ball or a rolling cylinder the damage on the back of the tape is reduced by the abrasion of the ball and the grinding belt. Also the abrasion of the ball is reduced. The counter-body can also be tribologically optimal coated for reducing the friction and the abrasion between the counter-body and the grinding belt.

Further advantageous coatings refer to the adjustment of the nano/micro topography of the grinding belt surface, which gets in contact to the sample surface, for instance through plasma or ion corrosion. The grinding belt can also be adhesively coated on the abrasive side, e g. by CVD or PVD methods like steaming or sputtering for being able to record an adhesive abrasion as well.

For evaluating the measurement a depth criterion can be used for example. In this case the abrasive belt runs until a certain depth criterion for the produced calotte in the sample surface is achieved. The depth criterion can be controlled by measuring the position of the counter-body after certain time distances or continuously. If the depth criterion is reached, the required space of time or the length of the belt, which was producing this calotte running through between the counter-body and the sample, can be determined. The space of time or the belt length now correlate with the wear resistance of the sample surface.

In the following an example of a device and a method according to the invention is described.

The only FIG. 1 shows a device for measuring the wear resistance of a sample body 1. The sample body 1 has a surface 10, on which a counter-body formed as hemisphere 4 is pressed. Between the counter-body 4 and the surface 10 of the sample body 1 an abrasive belt 3 is run through. This belt 3 is un-winded from a spool 6 a and wind up on a spool 6 b, while being transported by transport rolls 9, 9′ and run parallel to the surface 10 of the sample body 1 with the help of suppressing devices 8. A roll rail of that kind 6 a, 6 b, 8, 9, 9′ is to find for example in a conventional portable audio or videotape apparatus.

The hemisphere 4 is now fixed by a holding 5 referring to movements in the plane surface 10, although a holding 5 makes vertical movements of the hemisphere 4 to the surface 10 possible. The hemisphere 4 is furthermore connected to a unit 7, which puts a load on the hemisphere 4 and contains a measurement unit for determining the vertical position of hemisphere 4.

By unit 7 the hemisphere 4 is now pressed with a defined force on the magnet belt 3, so that it gets in friction contact to the surface 10 of the sample body 1 and produces a wear or abrasion calotte 2 during the run of the belt. On FIG. 1 the depth of the wear calotte 2 is presented exaggeratedly compared to the thickness of the tape 3 as usually the thickness of the tape is thousand times bigger than the depth of the produced calotte (with a depth of down to 1 nm).

The measuring unit 7 contains here for example an interferometer, which sends a ray of light on the plane surface of the hemisphere 4, which is turned away from the grinding belt. The ray of light is reflected from that surface and measured in the interferometer 7. From this measurement the position of the hemisphere 4 and, with timely distanced measurements, even the depth respectively the change of depth of the calotte 2 can be determined. 

1-28. (canceled)
 29. A method for determining wear resistance of a material surface object sample, comprising the steps of: running an abrasive grinding belt between a sample object and a counter-body; pressing said abrasive grinding belt with said counter-body by applying a predetermined force against said sample object; determining at least a first position and a second position of said counter-body at, at least, a first point in time and a second point in time, respectively, while said running said abrasive grinding belt between said sample object and said counter-body; calculating wear resistance of said sample object by measuring a difference in distance between, at least, said first position and said second position of said counter-body.
 30. The method for determining wear resistance of a material surface object sample according to claim 29, wherein said step of at least said first position and said second position of said counter-body is carried out by running backward said abrasive grinding belt, so that said first position is the same as said second position.
 31. The method for determining wear resistance of a material surface object sample according to claim 29, wherein said step of at least said first position and said second position of said counter-body is carried out by magnetic markings.
 32. The method for determining wear resistance of a material surface object sample according to claim 29, wherein said step of at least said first position and said second position of said counter-body is carried out on a continuous basis.
 33. The method for determining wear resistance of a material surface object sample according to claim 29, wherein said step of pressing said abrasive grinding belt with said counter-body by applying a predetermined force against said sample object is carried out by moving said counter-body vertically relative to a surface of said abrasive grinding belt.
 34. The method for determining wear resistance of a material surface object sample according to claim 29, wherein said step of pressing said abrasive grinding belt with said counter-body by applying a predetermined force against said sample object is carried out by fixing said first position of said counter-body and moving said abrasive grinding belt within the plane of a surface of said abrasive grinding belt.
 35. The method for determining wear resistance of a material surface object sample according to claim 29, wherein said step of determining at least a first position and a second position of said counter-body is performed capacitatively.
 36. The method for determining wear resistance of a material surface object sample according to claim 29, wherein said step of determining at least a first position and a second position of said counter-body is performed inductively.
 37. The method for determining wear resistance of a material surface object sample according to claim 29, wherein said step of determining at least a first position and a second position of said counter-body is performed optical interometrically.
 38. The method for determining wear resistance of a material surface object sample according to claim 29, wherein said counter-body is a ball.
 39. The method for determining wear resistance of a material surface object sample according to claim 29, wherein said counter-body is a cylinder.
 40. The method for determining wear resistance of a material surface object sample according to claim 29, wherein said step of pressing said abrasive grinding belt with said counter-body is carried out by using a mass of said abrasive grinding belt.
 41. The method for determining wear resistance of a material surface object sample according to claim 29, wherein said step of pressing said abrasive grinding belt with said counter-body is carried out by using means for applying a predetermined force for pressing said abrasive grinding belt.
 42. The method for determining wear resistance of a material surface object sample according to claim 41, wherein said means for applying a predetermined force for pressing said abrasive grinding belt is a mechanical compensation system.
 43. The method for determining wear resistance of a material surface object sample according to claim 42, wherein said mechanical compensation system is a see-saw.
 44. The method for determining wear resistance of a material surface object sample according to claim 41, wherein said means for applying a predetermined force for pressing said abrasive grinding belt is an inductive force generating system.
 45. The method for determining wear resistance of a material surface object sample according to claim 41, wherein said means for applying a predetermined force for pressing said abrasive grinding belt is a magnetic force generating system.
 46. The method for determining wear resistance of a material surface object sample according to claim 41, wherein said means for applying a predetermined force for pressing said abrasive grinding belt is a capacitative force generating system.
 47. The method for determining wear resistance of a material surface object sample according to claim 29, wherein said counter-body is a tribologically-optimized counter-body for reducing friction and wear between said counter-body and said abrasive grinding belt.
 48. An apparatus for determine wear resistance of a material surface object sample, comprising: an abrasive grinding belt; means for retaining and transporting said abrasive grinding belt over a material surface object sample; a counter-body; means for retaining and moving said counter-body; means for pressing said counter-body upon a surface of said abrasive grinding belt; and, means for measuring a position of said counter-body from a first position to a second position.
 49. The apparatus for determine wear resistance of a material surface object sample according to claim 48, wherein said means for measuring a position of said counter-body measures said first position and said second position at, at least, two different points in time.
 50. The apparatus for determine wear resistance of a material surface object sample according to claim 48, wherein said means for measuring a position of said counter-body measures said first position and said second position on a continuous basis.
 51. The apparatus for determine wear resistance of a material surface object sample according to claim 48, further comprising means for marking said first position and said second position of said counter-body and means for subsequently recognizing said marking of said first position and said second position of counter-body.
 52. The apparatus for determine wear resistance of a material surface object sample according to claim 48, wherein said means for retaining and moving said counter-body vertically moves said counter-body relative to the surface of said abrasive grinding belt.
 53. The apparatus for determine wear resistance of a material surface object sample according to claim 48, wherein said means for retaining and moving said counter-body fixes movement of said counter-body relative to the surface of said abrasive grinding belt.
 54. The apparatus for determine wear resistance of a material surface object sample according to claim 48, wherein said means for measuring a position of said counter-body is a capacitative measuring device.
 55. The apparatus for determine wear resistance of a material surface object sample according to claim 48, wherein said means for measuring a position of said counter-body is an inductive measuring device.
 56. The apparatus for determine wear resistance of a material surface object sample according to claim 48, wherein said means for measuring a position of said counter-body is an optically interometrical measuring device.
 57. The apparatus for determine wear resistance of a material surface object sample according to claim 48, wherein said counter-body is a cylinder.
 58. The apparatus for determine wear resistance of a material surface object sample according to claim 48, wherein said counter-body is a ball.
 59. The apparatus for determine wear resistance of a material surface object sample according to claim 48, wherein said means for pressing said counter-body upon the surface of said abrasive grinding belt is a force-generating system.
 60. The apparatus for determine wear resistance of a material surface object sample according to claim 59, wherein said force-generating system is a mechanical compensation device.
 61. The apparatus for determine wear resistance of a material surface object sample according to claim 60, wherein said mechanical compensation device is a see-saw.
 62. The apparatus for determine wear resistance of a material surface object sample according to claim 59, wherein said force-generating system is an inductive force-generating system.
 63. The apparatus for determine wear resistance of a material surface object sample according to claim 59, wherein said force-generating system is a magnetic force-generating system.
 64. The apparatus for determine wear resistance of a material surface object sample according to claim 59, wherein said force-generating system is a capacitative force-generating system.
 65. The apparatus for determine wear resistance of a material surface object sample according to claim 49, wherein said counter-body is a tribologically-optimized counter-body for reducing friction and wear between said counter-body and said abrasive grinding belt. 